Wavefront sensors are devices used to measure the shape of a wavefront of light (see, for example, U.S. Pat. No. 4,141,652 and U.S. Pat. No. 5,164,578). In most cases, a wavefront sensor measures the departure of a wavefront from a reference wavefront or an ideal wavefront such as a plane wavefront. A wavefront sensor can be used for measuring both low order and high order aberrations of various optical imaging systems such as the human eye (see for example, U.S. Pat. No. 6,595,642; J. Liang, et al. (1994) “Objective measurement of the wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor,” J. Opt. Soc. Am. A 11, 1949-1957; T. Dave (2004) “Wavefront aberrometry Part 1: Current theories and concepts” Optometry Today, 2004 Nov. 19, page 41-45). Furthermore, a wavefront sensor can also be used in adaptive optics in which the distorted wavefront can be measured and compensated in real time, using, for example, an optical wavefront compensation device such as a deformable mirror (see for example U.S. Pat. No. 6,890,076, U.S. Pat. No. 6,910,770 and U.S. Pat. No. 6,964,480). As a result of such compensation, a sharp image can be obtained (see for example U.S. Pat. No. 5,777,719).
The term “phakic eye” refers to an eye including its natural lens, the term “aphakic eye” refers to an eye with its natural lens removed and the term “pseudo-phakic eye” refers to an eye with an artificial lens implanted. Currently, most wavefront sensors for measuring the aberration of a human eye are designed to only cover a limited diopter range of about −20D to +20D for a phakic or pseudo-phakic eye. In addition, they are also designed to operate in a relatively dark environment when the eye wavefront is to be measured.
During ophthalmic surgeries that affect refraction, it is desirable to know the refractive state of the eye as the surgery is on-going so that a continuous feedback can be provided to the surgeon (see for example, U.S. Pat. No. 6,793,654, U.S. Pat. No. 7,883,505 and U.S. Pat. No. 7,988,291). This is especially the case in cataract surgery in which the natural lens of the eye is replaced by a synthetic lens. In such a case, the surgeon prefers to know the refractive state of the eye in the phakic, aphakic and pseudo-phakic stage in order to select a synthetic lens, confirm if its refractive power is correct after the natural lens is removed, and also to confirm emmetropia or other intended diopter values after the synthetic lens is implanted. Therefore, there is a need for a wavefront sensor to cover a larger diopter measurement range and also to allow the surgeon to measure the refractive state of the eye, with a specified degree of precision, at not only the phakic and pseudo-phakic state but also at the aphakic state.
Also during ophthalmic surgery, the eye is illuminated with unpolarized broadband (white) light from the surgical microscope so the surgeon can see the patient eye through the microscope. This illuminating light is also directed into the eye of the patient, scattered from the retina, and returned to the surgical microscope. A wavefront sensor coupled to the surgical microscope receives both its intended returned wavefront measurement light and the broadband illumination from the surgical microscope. The microscope illumination light source is generally not designed to produce a sufficiently-small effective source of light at the retina that is required to generate a wavefront that reveals the patient's refractive state. Because of this, any illumination light from the surgical microscope that is accepted by the wavefront sensor can lead to incorrect information about the patient's refractive state. Therefore, there is also a need for an ophthalmic wavefront sensor that is immune to influence of the illumination light from a surgical microscope.
Commercially available wavefront sensors for cataract surgery, such as the ORange intraoperative wavefront aberrometer from WaveTec Vision (see for example, U.S. Pat. No. 6,736,510), do not provide continuous feedback, are limited in refractive diopter range coverage and also are not immune to interference from the illumination light of the surgical microscope. In fact, in order to get a sufficiently precise and accurate refraction measurement using the ORange wavefront sensor, the surgeon has to pause the surgical procedure, turn off the illumination light of the surgical microscope, and has to capture multiple frames of data, which leads to additional time up to several minutes added to the cataract refractive surgery time.